A typical propulsion device for an outboard marine motor includes a drive shaft extending vertically within a gear casing and connecting to a crank shaft of an internal combustion engine at an upper end. A drive bevel gear is fixably attached to a lower end of the drive shaft. A propeller shaft extends horizontally adjacent to the lower end of the drive shaft with a pair of driven bevel gears supported coaxially to the propeller shaft in a freely rotatable manner and meshing with the drive bevel gear so as to rotate in mutually opposite directions. A pair of clutch devices engage a selected one of the driven bevel gears with the propeller shaft. A prop shaft holder is secured to a gear casing for supporting and positioning the propeller shaft and a propeller is connected for co-rotation with the propeller shaft.